Angioplasty is an efficient and successful method of opening stenosis in the vascular system. In a popular form of angioplasty, a balloon catheter is advanced through the vascular system until the balloon, which is carried at the distal end of a catheter shaft, and which may carry an expandable stent, is positioned across the stenosis or damaged vessel. By inflating the balloon pressure is applied to the obstruction, which is moved by pressing it against the inner wall of the vessel, whereby the vessel is opened for improved flow. Due to the expansion of the balloon, the stent, which—if used—is situated on the balloon, is also expanded for aiding in repairing the vessel wall and hindering obstruction. As a last step the stent is then released by deflating the balloon reducing its circumference until refolding of the balloon occurs followed by removal of the balloon and catheter from the vessel along a guide wire.
There are various types of balloon catheters. One type is fed over a guide wire (i.e., “over-the-wire” catheters) and another type serves as its own guide wire (“fixed-wire” catheters). There have been developments of variations of these two basic types: the so-called “rapid exchange” type, “innerless” catheters, and others.
In another popular form of angioplastie selfexpanding stents are delivered to the target site in a vessel via a self-expanding stent delivery catheter. Usually the stent is covered by a sheath to keep it in the contracted configuration on the catheter until it reaches the target side. The sheath is then retracted in order to release the stent and the catheter is subsequently removed from the vessel.
If a catheter, like a balloon catheter, is used in percutaneous transluminal angioplasty (PTA) or percutaneous transluminal coronary angioplasty (PTCA), it is typically advanced through a guide catheter to a preselected vessel location, such as the aorta, for example. Using an imaging technique like fluoroscopy or MRI, the surgeon advances the catheter until the balloon is located across the stenosis or obstruction. This may involve the use of a guide wire over which the catheter is moved or alternatively the catheter may act as its own guide wire. Besides the fact that a smooth advancement in the vessels is in itself very advantageously, a possible origin of trouble arriving from this advancement of the catheter is the friction between the wire and the inner lumen of the catheter when guiding the catheter along the wire. As the movement in the vessels is highly difficult and a task requiring great handling skills any resistance in addition to those unavoidable due to the nature of the vessels being penetrated is strictly unwanted. Accordingly besides smoothness of the catheter (tip) itself a smooth movement of the wire inside the catheter avoiding as much friction as possible is highly desired. However, on the other hand the catheter needs sufficient pushability in order to advance the catheter over for example a stenosis in the vessel.
In order to address these conflictive needs, high flexibility and high pushability, many catheters, in particular PTA or PTCA catheters include a proximal portion that is relatively stiff, conventionally made from a stainless steel hypotube and a transition to a relatively soft and flexible distal portion of the catheter conventionally made from polymeric materials like PEBAX or Nylon.
Further, diagnostic catheters which are commonly used to facilitate the diagnosis of vascular diseases such as coronary artery disease and peripheral vascular disease and guide catheters which are commonly used to facilitate advancement of a PTA or PTCA catheter to the treatment site within the vessel when treating vascular diseases, commonly include a metallic braid reinforcement layer disposed between an inner layer and an outer layer. The braid reinforcement provides torsional rigidity, column strength, kink resistance, as well as radiopacity and is conventionally made from stainless steel wire.
However, a major drawback of these conventional braid reinforcement materials and hypotube materials such as stainless steel is their incompatibility with MRI (magnetic resonance imaging) due to their ferro-magnetic properties. MRI has become a standard in non-invasive diagnostic imaging and it is expected that MRI will be used in the future also for endovascular diagnosis and even treatment. The benefit for the patient compared to currently used x-ray angiogram is the absence of γ ray exposure and the use of less impacting contrast media.
Therefore, there is a clear need for improved high strength materials especially tubes for medical devices that allow use of these medical devices for effective treatment of the patient. There is a strong need for biocompatible and MRI compatible materials providing sufficient strength and elasticity.